U.S. patent application number 09/832094 was filed with the patent office on 2001-11-22 for random access control method for cdma system.
Invention is credited to Nakada, Suguru.
Application Number | 20010043582 09/832094 |
Document ID | / |
Family ID | 18653048 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043582 |
Kind Code |
A1 |
Nakada, Suguru |
November 22, 2001 |
Random access control method for CDMA system
Abstract
An object of the present invention is to provide an efficient
channel access method on the base of propagation delay times in a
random access system. The access control method of the present
invention for CDMA system wherein a base station is connected with
a plurality of mobile stations by the random access is
characterized in that the base station stores the propagation delay
time of the preamble signal into a memory unit, when the base
station transmits a rejection signal for rejecting a communication
toward the mobile station which transmits the preamble signal.
Further, the base station transmits a allowance signal for allowing
a communication toward the mobile station of which propagation
delay time is substantially equal to that stored in the memory in
the base station.
Inventors: |
Nakada, Suguru; (Tokyo,
JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Family ID: |
18653048 |
Appl. No.: |
09/832094 |
Filed: |
April 11, 2001 |
Current U.S.
Class: |
370/335 ;
370/342 |
Current CPC
Class: |
H04B 7/2628
20130101 |
Class at
Publication: |
370/335 ;
370/342 |
International
Class: |
H04B 007/216 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2000 |
JP |
2000-146752 |
Claims
What is claimed is:
1. A random access control method for a CDMA system comprising a
base station and a plurality of terminals, which comprises the
steps of: receiving at said base station preamble signals from said
terminals; transmitting to said terminals signals for allowing said
random access or signals for rejecting said random access; and
storing propagation delay times for said terminals of which random
access are rejected.
2. The random access control method according to claim 1, wherein
transmission data in a message part transmitted by each of said
terminals of which random access are allowed is received by said
base station.
3. The random access control method according to claim 1, wherein
said base station gives a priority to such a terminal that a
present propagation delay time of that terminal is substantially
equal to one of the stored propagation delay time.
4. The random access control method according to claim 1, wherein
said base station: gives a priority to one of said terminals on the
basis of an electric power, Eb/NO ratio, or a data error rate in
addition with said propagation delay time; and stores said electric
power, Eb/NO ratio, or data error rate in addition with said
propagation delay time for said terminal of which random access is
rejected.
5. A base station apparatus for controlling a plurality of
terminals in a random access CDMA system, which comprises: a
receiving unit for receiving the preamble signals and transmission
data from said terminals of which random accesses are allowed; a
correlation unit for calculating a correlation between an output
from said receiving unit and a plurality of prescribed preamble
signals; a preamble signal determination unit for determining
whether the base station transmits a signal for allowing said
random access or a signal for rejecting said random access on the
basis of said correlation and a propagation delay time of said
preamble said the propagation delay time; and a code generation
unit for generating and transmitting said signal for allowing said
random access or said signal for rejecting said random access.
6. The base station apparatus according to claim 5, which further
comprises a delay memory unit for storing said delay time of said
terminal of which random access is rejected.
7. The base station apparatus according to claim 5, wherein said
base station: transmits to one of said terminals said signal for
allowing said random access; stores propagation delay times of said
terminal of which random access are rejected; and gives a priority
to such a terminal that a present propagation delay time of that
terminal is substantially equal to one of the stored propagation
delay times.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates to a method and circuit for
controlling channels in random accesses by using preamble signals
under CDMA in order to allocating efficiently access channels
particularly for mobile communication systems.
[0003] 2. Description of the Prior Art
[0004] A control channel is independent upon communication channel
in the conventional mobile communication system. A base station
controls mobile stations through the control channels, when a call
occurs. Here, a plurality of base stations are provided in a wide
service area. Further, a common frequency is used for the
communication channels for zones which are distant enough to
neglect interference noises. Thus, frequency resource is used
efficiently.
[0005] The frequency may also be common for the control channel in
the zones which are distant enough to neglect interference
noises.
[0006] In JP 3-6932 A (1991), the mobile station transmits a
control signal of which header designates an object base station.
On the other hand, the base station transmits a free cannel signal
for allowing the mobile station to transmit the control signal and
an identifier for the base station. When the identifier is
identical with that transmitted by the mobile station, the base
station stops transmitting the free channel signal, thereby knowing
immediately whether or not the mobile station stays in its zone.
Thus, the channel is efficiently controlled.
[0007] Further, in JP 8-167885, a pseudo carrier pulse is
transmitted into a radio channel network, by determining whether
any carrier is transmitted or not. Further, a channel number for a
data packet is confirmed, and channel allocation is controlled,
when a plurality of communication terminals uses a channel
competitively. Further, data items from the communication terminals
are determined and two-stepped priorities are set up on the basis
of the determination result.
[0008] Further, in JP 10-178386 A (1998), transmission management
unit 44 as shown in FIG. 6 modulates packets with a preamble and
data generated by down stream signal generation unit 45. The
modulated packets are transmitted through duplexer 42 by antenna
41, in a random access CDMA system. A down stream standard signal
which is as long as the preamble may also be transmitted.
[0009] Communication terminal 30 receives the down stream standard
signal through antenna 31 and duplexer 32 by using receiving unit
33. The downstream standard signal is detected by transmission
timing pickup unit 35, thereby executing the random access by using
transmission unit 34 on the basis of detected transmission timing
signal.
[0010] Delay profile measurement unit 47 in base station 40
calculates a correlation between the preamble and a pseudo-noise
code in order to obtain a delay profile in the basis of cyclic
addition for reducing noises. The timing signal outputted from
delay profile measurement unit 47 is inputted into despreading
management units 48.sub.1.about.48.sub.3 which demodulates the
received signal by despreading it by using the pseudo-noise code
synchronized with the timing signal.
[0011] Thus, RAKE reception can be executed by the outputs from
despreading management units 48.sub.1.about.48.sub.3, when the
packet with preamble and data is modulated by a short period
pseudo-noise. On the other hand, when the packet is modulated by a
long period pseudo-noise in the slotted ALOHA system, the delay
time can be estimated, the synchronous timing can be acquired,
thereby reducing transmission power, separating long delay
profiles, and executing the random access.
[0012] Further, in JP 2000-59850 A, an additional bandwidth is
allocated fairly and efficiently in a cellular communication system
for transmitting and receiving data burst between mobile
stations.
[0013] Furthermore, the conventional CDMA mobile communication
system includes a random access system which uses upward random
access link channel, or RACH (random access channel).
[0014] RACH as shown in FIG. 5 comprises preamble signal 28 and
message part 30. Message part 30 is used for transmitting actual
information, while preamble signal 28 is used for a request signal
for obtaining the message part from a mobile station. In other
words, preamble signal is used by mobile stations for requesting a
right of using the message part which are commonly used by all the
mobile stations.
[0015] Therefore, the base station has to allocate the finite
message part resource, when a plurality of mobile stations request
simultaneously the right of using the message part. In this case,
one or more mobile stations are rejected inevitably in the random
access system. Therefore, it is desirable to give a priority to the
mobile station which was once rejected, in order to avoid a long
time wait of that mobile station which was once rejected.
[0016] Accordingly, the base station may store the identifiers of
the once rejected mobile stations, compare the identifiers with the
calling mobile stations, and give a priority to the mobile station
of which identifier is stored in the base station. The simplest
identifier may be the preamble signal, because its length is
constant. However, the preamble can not always be used in every
CDMA mobile communication system. For example, the preambles of
RACH in W-CDMA expectedly introduced in the year 2001 are only ten
or more. The mobile station selects randomly one preamble among the
ten or more preambles, when the mobile station transmits the
preamble. Therefore, the base station can not identify the mobile
station by such preambles. Accordingly, other kind of identifier is
required.
[0017] The propagation delay time is employed in the present
invention, because the propagation delay time depending upon a
position and environment of the mobile station is measures
correctly in the CDMA system and therefore useful to identify the
mobile station.
SUMMARY OF THE INVENTION
[0018] An object of the present invention is to control efficiently
the channel access on the basis of the propagation delay time.
[0019] The access method of the present invention for CDMA system
wherein a base station is connected with a plurality of mobile
stations by the random access is characterized in that the base
station stores the propagation delay time of the preamble signal
into a memory unit, when the base station transmits a rejection
signal for rejecting a communication toward the mobile station
which transmits the preamble signal.
[0020] Further, the base station transmits an allowance signal for
allowing a communication toward the mobile station of which
propagation delay time is equal to that stored in the memory in the
base station.
[0021] The base station apparatus of the present invention
comprises a receiving unit for receiving the preamble signal and
transmission data from the base station which receives the
allowance signal, a correlation unit for calculating a correlation
between a plurality of prescribed standard preamble signal and a
base band signal outputted from the receiving unit, a preamble
signal determination unit for determining whether the base station
transmits the rejection signal or the allowance signal on the basis
of the correlation and the propagation delay time, a code
generation unit for generating the rejection signal or the
allowance signal on the basis of the determination result, and a
transmission unit for transmitting the rejection signal or the
allowance signal.
[0022] In short, the present invention provides an efficient
control for a random access by preamble signal in CDMA (code
division multiple access) system for mobile communication.
[0023] According to the present invention, the base station which
controls random accesses from a plurality of communication
terminals gives a priority to the once rejected terminal which
requests the access again, as long as there is any available
message part. Therefore, the maximum waiting time for obtaining a
message part can be reduced, thereby easing a heavy traffic wherein
calls are not connected for however long time the calls are
requested.
BRIEF EXPLANATION OF THE DRAWINGS
[0024] FIGS. 1A and 1B are illustrations of the CDMA system of the
present invention.
[0025] FIG. 2 is a block diagram of a part of the base station in
the CDMA system of the present invention.
[0026] FIG. 3 is a sequence diagram for explaining the operation of
the CDMA system of the present invention.
[0027] FIG. 4 is a flow chart for explaining the operation of the
CDMA system of the present invention.
[0028] FIG. 5 is a frame structure in a conventional random access
CDMA system.
[0029] FIG. 6 is a block diagram of a conventional random access
CDMA system.
PREFERRED EMBODIMENT OF THE INVENTION
[0030] The embodiment as shown in FIGS. 1A and 1B is a CDMA mobile
communication system wherein communication terminals 2, 3 and 4
transmit the preamble signals consisting of a plurality of codes
for obtaining the message part.
[0031] Transmitter/receiver of base station 1 in the base station
is provided with memory means for storing the propagation delay
times of the preamble signals, together with other units in the
conventional base station 40 as shown in FIG. 6.
Transmitter/receiver of base station 1 receives the preamble
signals from a plurality of communication terminals 2 to 4, and
transmits the allowance signal (ACK signal), or the rejection
signal (NACK signal), on the basis of each preamble signal.
[0032] A plurality of preamble signals which are used commonly by
the communication terminals are prescribed beforehand. However, any
specific preamble is not prescribed for each mobile station.
Further, every time the communication terminal transmits a
preamble, the preamble is not the same as that used at the last
occasion. Therefore, transmitter/receiver of base station 1 in the
base station can not identify the communication terminal merely by
analyzing the signal sequence of the preamble.
[0033] FIG. 2 is a block diagram of a channel access unit in
transmitter/receiver of base station 1 as shown in FIG. 1. A base
band signal demodulated by a demodulator is inputted into
correlation unit 13, while a base band signal before being
modulated by a modulator is outputted from code generation unit 15.
Correlation unit 13 comprises a despreading unit for despreading a
spread spectrum signal and a transmission channel estimation unit
for estimating a transmission channel of the received signal which
propagates via a plurality of transmission channels.
[0034] Correlation unit 13 calculates correlations between preamble
signals selected among a plurality of prescribed preamble signals
and a despread base band signal, and then outputs the correlation
values and the propagation delay times. Here, The number of
prescribed preamble signals may be sixteen, and the prescribed
preamble signal may be a pseudo noise code for spread spectrum
system. Ordinarily, a signal with a preamble rarely reaches
simultaneously together with other signal with that preamble.
However, it is important to avoid any collision. The number of
correlation units 13 is the number of the mobile stations covered
by a base station or the number of the mobile stations which are
prescribed and can be received by a base station. Correlation unit
13 obtains a propagation delay time of a preamble signal on the
basis of a delay profile which is a graph of signal level versus
delay time. For example, the delay time may be a shift of the
received preamble from the stored preamble.
[0035] Preamble determination unit 14 determines whether a preamble
was received or not, and then determines whether ACK should be
transmitted or NACK should be transmitted. Only one preamble
determination may be employed, even when a plurality of correlation
units 13 are employed. The output from correlation unit 13, or a
information pair of a mobile station transmitting a preamble and a
delay time of that preamble, is stored if necessary by preamble
determination unit 14.
[0036] Code generation unit 15 generates ACK signal or NACK signal
on the basis of the output from preamble determination unit 14 and
outputs the ACK signal or the NACK signal toward the modulator in
the transmission unit. Delay memory unit 16 stores for a prescribed
time period the delay time of the preamble signal for which the
NACK signal is replied. Delay memory unit 16 may be a one chip
SRAM, one chip DRAM, or a plurality of registers.
[0037] The combination of correlation unit 13 and preamble
determination unit 14 as shown in FIG. 2 is a part of delay profile
measurement unit 47 as shown in FIG. 6, while delay memory unit 16
as shown in FIG. 2 is a memory of delay profile measurement unit
47. The timing signal from timing generation unit 46 as shown in
FIG. 6 is inputted into correlation unit 13 as shown in FIG. 2.
[0038] The operation of the embodiment of the present invention is
explained, referring to the block diagram as shown in FIG. 1 and
the flow chart as shown in FIG. 3.
[0039] It is assumed that preamble signals for requesting a message
part are transmitted simultaneously by communication terminals 2
and 3. Transmitter/receiver of base station 1 receives preamble
signals 5 and 6. However, transmitter/receiver 1 can not identify
the communication terminals on the basis of the preambles. At step
S21, transmitter/receiver of base station 1 determines whether it
can allocate a message part or not for the communication terminals
which transmitted the preambles. Only one communication terminal is
qualified for the allocation, if there is only one free message
part.
[0040] It is further assumed that the message part is allocated for
communication terminal 3 which transmitted preamble signal 6, while
the message part is not allocated for communication terminal 2
which transmitted preamble signal 5. In this case, ACK signal 8 for
allowing to use the message part is transmitted for preamble signal
6. Therefore, communication terminal 3 can access the message part
at step S26. On the other hand, NACK signal 7 for rejecting to use
the message part is transmitted for preamble signal 5. In this
case, the propagation delay of preamble signal 5 is stored at step
S22. Thus, communication terminal 3 which are allowed to use the
message part can transmit and receive digital signal of voice,
picture, or data.
[0041] After transmitting the preambles as shown in FIG. 1, it is
assumed that communication terminals 2 and 4 transmits preambles,
respectively. It is also assumed that preamble signal 9 from
communication terminal 2 is different from preamble signal 5 as
shown in FIG. 1A. Thus, transmitter/receiver of base station 1
receives preamble signals 9 and 10. If only one message part is
available, transmitter/receiver reads out the propagation delay of
preamble signal 5 for which NACK signal is replied before at step
S23 in order to compare the read-out propagation delay with the
delay times of preamble signals 9 and 10.
[0042] Then, transmitter/receiver of base station 1 gives a
priority to the preamble signal of which propagation delay is equal
to or approximately equal to the propagation delay of preamble
signal 5 at step S24. Thus, it is avoided that once rejected
communication terminal is rejected repeatedly. Transmitter/receiver
of base station 1 can identify the once rejected communication
terminal, when the first delay is substantially equal to the second
delay, even if there is any small difference between them.
[0043] Therefore, when the propagation delay of preamble signal 9
is substantially equal to the propagation delay of preamble 5,
transmitter/receiver of base station 1 deems that a communication
terminal transmitted preambles 9 and 5, and gives a priority to
that mobile station. Accordingly, ACK signal 11 is transmitted for
preamble 9, while NACK signal 12 is transmitted for preamble
10.
[0044] Finally, at step S25, transmitter/receiver of base station 1
deletes the stored propagation delay of preamble signal 5, while it
stores newly the propagation delay of preamble 10 which is
rejected. Thus, the above-explained steps are repeated.
[0045] The operation of the channel access control unit as shown in
FIG. 2 is explained, referring to the flow chart as shown in FIG.
4. At first at step S11, the demodulated base band signal is
inputted into correlation unit 13. Correlation unit 13 calculates a
time correlation between the base band signal and each of
prescribed preamble signals. Then, the highest correlation value
and its propagation delay are outputted toward preamble
determination unit 14 at step S12.
[0046] A threshold is prescribed by preamble determination unit 14,
thereby filtering out the correlation smaller than the threshold.
Preamble determination unit 14 decides an order of priority for the
correlations which is greater than the threshold on the basis of
the correlation values and the propagation delays. Then, at step
S13, the present propagation delay is compared with propagation
delays of lower priority preamble signals stored in delay memory
unit 16.
[0047] When the present propagation delay is substantially equal to
the stored propagation delay of the lower priority preamble
signals, preamble determination unit 14 gives higher priorities to
the lower priority preamble signals. Then, at step S17, ACK signal
and NACK signals are generated at step S16 and are outputted to the
modulator.
[0048] Then, at step S18, it is checked whether NACK signal is
transmitted. If NACK was transmitted, the propagation delay of the
preamble signal for which NACK was transmitted is stored in delay
memory unit 16 at step S19.
[0049] The stored propagation delay is used when the priority is
decided afterward.
[0050] The priority may be decided on the basis of the propagation
delay and an electric power of the received signal. In this case,
ACK signal is transmitted toward the communication terminal of
which electric power is the greatest, when the propagation delay is
almost the same for the communication terminals, because the
highest power terminal can executes a reliable communication.
Further, the priority may also be decided on the basis of the
propagation delay, the electric power, Eb/NO ((energy/bit)/noise
spectrum density) and data error rate of preamble signal. In this
case, electric power, Eb/NO, and data error rate are stored in
delay memory unit 16 for the rejected preamble signals for which
NACK signals are transmitted.
[0051] The present invention is also applicable to a dispersed
system without base station control, an in-house wireless LAN,
spread spectrum system in general, a system wherein propagation
delays can be measured, a wireless LAN such as WLL (wireless local
loop), or Bluetooth system for small area propagation using small
power.
[0052] The base station in the present invention may be a switching
station connected with other base stations. The base station may be
connected with a public telephone network.
* * * * *